Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$13.52	13.628%	$15.3625	$15.36	$15.35	$15.40
Purchase #2	$141.56	9.847%	$155.4994	$155.50	$155.50	$155.50
Purchase #3	$230.47	12.822%	$260.0209	$260.02	$260.00	$260.00
Purchase #4	$39.27	3.199%	$40.5262	$40.53	$40.55	$40.50
Purchase #5	$87.37	4.104%	$90.9557	$90.96	$90.95	$91.00
Purchase #6	$67.62	10.592%	$74.7823	$74.78	$74.80	$74.80
Purchase #7	$179.61	11.522%	$200.3047	$200.30	$200.30	$200.30
7 purchase totals =	$759.42		$837.4517	$837.45	$837.45	$837.50